diff --git a/setup/extensions.py b/setup/extensions.py
index d309f5fa4f..f9038d2624 100644
--- a/setup/extensions.py
+++ b/setup/extensions.py
@@ -95,6 +95,7 @@ extensions = [
 
     Extension('monotonic',
         ['calibre/utils/monotonic.c'],
+        libraries=['rt'] if islinux else [],
         ),
 
     Extension('speedup',